German Chancellor Angela Merkel said on Thursday her coalition would field Lower Saxony state premier Christian Wulff as its candidate for president after Horst Koehler shocked the country with his resignation.

Wulff, 50, is widely seen as a moderate conservative and would be unlikely to rock the boat as president, a largely ceremonial post.

But Merkel, beset by a slump in popularity and a drubbing in a state election last month, still faces a crucial challenge in getting him elected in a vote by a special parliamentary assembly to be held on June 30.

While it is likely that she will get her choice through the assembly, where her centre-right coalition has a majority, any hiccup would seriously undermine her already waning authority.

"I am especially happy that (Wulff) is ready to take over this responsibility for our country, at a time when we are faced with a global economic crisis and when the future of Europe is at stake," Merkel said at a news conference in Berlin.

"I think we can offer the parliamentary assembly a very good candidate who will certainly get a lot of approval."

Rival candidate 

The Social Democrat and Greens opposition parties said on Thursday they were putting forward a rival candidate for president -- Joachim Gauck, 70, who headed research into the Stasi archives after the collapse of communism.

Merkel's candidate, Wulff, 50, is a heavyweight in her Christian Democrats (CDU) and a loyal ally.

The trained lawyer leads a coalition of conservatives and Free Democrats in Lower Saxony, reflecting the formation of the national government. With the candidacy, Merkel may want to send a signal that the alliance is still a force to be reckoned with.

Koehler, a former head of the International Monetary Fund, stood down on Monday after a wave of criticism over comments he made to justify German military action abroad.

His resignation was a blow to Merkel, whose conservative bloc has seen its support drop to 30 percent, the lowest level in nearly four years, according to a new poll.

His departure, coupled with last week's exit from politics of Hesse state premier Roland Koch, a prominent ally who leaves a gap on the right of the conservative camp, has given the impression of rats abandoning a sinking ship, say commentators.

Merkel said she tried to persuade Koehler to stay and is reported to have warned him that resigning could trigger a crisis and even shake public faith in state institutions.

Wulff is seen as a consensus candidate and has been mentioned as a possible future chancellor but ruled himself out in 2008, saying he was not enough of an "alpha male".

Reuters